Y. Wu, Y. Yao, F. Xu, H. Tong, and J. Lu. Proceedings of the 25th ACM International on Conference on Information and Knowledge Management, page 2287--2292. New York, NY, USA, ACM, (2016)
M. Ester, H. Kriegel, J. Sander, and X. Xu. Proc. of 2nd International Conference on Knowledge Discovery and Data Mining (KDD-96), page 226-231. (1996)